The use and development of carbon nanotubes has expanded, as these materials have shown to be valuable in next generation industries including the fields of electronics and chemistry. The further development of carbon nanotube technology allows organized structures or intertwined randomly oriented bundles of carbon nanotubes to be formed. Techniques have been developed to controllably build organized architectures of nanotubes having predetermined orientations, such as vertically aligned nanotubes. Although such structures may be useful for a variety of purposes, the structures by themselves may be limited in terms of function and application.
In the area of adhesives for example, it would be desirable to provide dry adhesives which may be useful in a variety of applications and environments for which standard adhesives have deficiencies. Adhesives are typically wet and polymer-based, and have low thermal and electrical conductivity. For electronics, micro-electro-mechanical systems (MEMS), low or zero atmosphere environments, cryogenic or high temperature environments, or a variety of other areas, it would be desirable to provide a dry adhesive which is selectively attachable and detachable to/from a surface. It would also be desirable to provide an adhesive which has other beneficial properties, such as high electrical and thermal conductivity or high adhesion strengths while being selectively detachable. For example, the mechanism which allows a gecko lizard to climb a vertical surface or any other surface is based upon the anatomy of the gecko's feet and toes, wherein each five-toed foot is covered with microscopic elastic hairs called setae. The ends of these hairs split into spatulas which come into contact with the surface and induce enough intermolecular (van der WAALS, [VdW]) forces to secure the toes to the surface. The gecko's foot anatomy allows them to selectively adhere to any surface which they touch. Although attempts have been made to provide synthetic systems which mimic the gecko's feet and toe anatomy, no such systems have generally been successful. It would be desirable to provide an adhesive which mimics these characteristics, and provides a surface which interacts with other surfaces via intermolecular or VdW forces, via nanostructure technologies.
It has also been noted that the external surfaces of many plants and animals have a rough surface structure combined with an ideal surface chemistry to create self-cleaning, water-repellant surfaces. For example, the VdW interaction between the hairs of the gecko and a substrate after contact may play a role in self-cleaning. Additionally, self-cleaning characteristics are found on the leaf surface of the N. nucifera (the white lotus) and the wing surface of many insects, which combine a topology describing a high degree of surface roughness with a chemistry that exhibits low surface energy. Such a combination creates a superhydrophobic surface that sheds liquids of various types, and allows particulates to be removed when subjected to an external force such as rolling water droplets, or flowing air. It would be desirable to provide self-cleaning characteristics in association with adhesive type materials. Some other systems found in nature that exhibit self-cleaning properties include the leaves of the lotus and lady's mantle plants. It has also been found that the For example, the self-cleaning characteristics found on the leaf surface of the N. nucifera (the white lotus) and the wing surface of many insects combine a topology describing a high degree of surface roughness with a chemistry that exhibits low surface energy thus creating a superhydrophobic surface such that it sheds liquids of various types, allowing particulates to be removed when subjected to an external force such as rolling water droplet, or flowing air. The surface of the lotus leaves for example have two levels of microscopic roughness, which along with a hydrophobic wax coating, render the lotus leaves superhydrophobic. A water droplet, when placed on the surface of a lotus leaf, forms a large contact angle with low contact angle hysteresis. This results in the water droplets rolling off the leaf surface, leaving the surface clean. Leaves of a lady's mantle plant have hairs of 10 μm and a length of 1 mm. It has been noted that the individual hairs may be hydrophilic. However, when acting together on the surface, they make the surface of the leaves superhydrophobic. It would be desirable to provide self-cleaning characteristics in association with adhesive type materials, as well as other materials or products.
In a variety of other areas, the use of organized carbon nanostructures in unique configurations may provide valuable functions in self-cleaning adhesives, biocompatible or bioactive systems, electronic displays, functional films or skins, or other applications.